186 
IOWA ACADEMY OF SCIENCE Voi,. XXVIII, 1921 
cent (fig. 21), almost doubles it. The weakest concentration, 0.5 
vols. per cent, shows still an increased height of response above 
that of the normal, but when compared to the two preceding re- 
cords it is very evident that the optimum of stimulating effect 
has been passed, and that solutions of weaker strengths will be 
too dilute, and would show diminution of physiological effects. 
Aside from the height of the response, there are other interesting 
features of the curves which seem equally indicative of modified 
activity. If we note especially the form of the relaxation phase 
of the curves it is clear that a modification has been made here 
also. It changes successively from a maintained plateau in the 
strong solutions (figs. 27, 18) to a concaved form resembling the 
normal in lower strengths (figs. 20 and 21). Another interesting 
fact is brought out by applying a second stimulus in alcohol. We 
were able to obtain practically no secondary response in 40 and 
25 vols. per cent concentrations, but in the 10.0 vol. per cent and 
below we could restimulate and obtain a response which in each 
case was considerable and proportional to the height of the first. 
This fact, it seems to us, lends further proof as to the correctness 
of our interpretation. 
The effect of various concentrations of propyl alcohol is shown 
typically in successive series of somites of earthworm 101, figures 
28 to 31 inclusive. Carrying out the same procedure as just men- 
tioned, this alcohol yields interesting comparative data. On apply- 
ing 10 vols. per cent propyl, the normal response is cut to about 
one-fourth in height (fig. 28), which fact when compared with 
40 vols. per cent ethyl (fig. 27) is of value, when it is recalled 
that the computed toxicity of one member of the aliphatic series 
of alcohols is between three and four times that of its immediate 
predecessors.® When the concentration is reduced to 5.0 vols. 
per cent, the resulting response as shown in figure 29 is increased 
to about one-half of the normal height. In concentration of 1.0 
vol. per cent, the response is practically doubled (fig. 30) and 
dilution beyond this point results in a drop in height (fig. 31) 
exactly as described above in the case of ethyl alcohol. Com- 
parable differences were here also shown in the form of relaxation 
phase of the responses throughout, as well as a corresponding 
ability to respond to restimulation. These similarities are strik- 
ingly shown on comparing figures 27 and 28; 20 and 29; 21 and 
30; and 22 and 31. 
